This invention relates to gas turbine combustors and particularly to gas turbine combustors of the type having an upstream combustion chamber and a downstream combustion chamber interconnected by a venturi throat region.
A dry low NOx combustor is the subject of U.S. Pat. No. 4,292,801 to inventors Wilkes and Hilt which is assigned to the assignee of the present invention. In particular, that patent describes a gas turbine combustor which has an upstream combustion chamber and a downstream combustion chamber interconnected by a venturi throat region. There is an annular array of primary nozzles which input fuel into the upstream combustion chamber and a central nozzle which inputs fuel into the downstream combustion chamber. Low NOx (oxides of nitrogen) output is achieved, in part, by the method of operating the subject combustor which includes operating the combustor in a premix mode during the normal or base load such that the primary nozzles are flamed out but fuel is input through the primary nozzles to premix with combustion air whereupon the mixture is ignited in the downstream combustor chamber by the central nozzle. To achieve success in lowering NOx output in the combustor design it is important that fuel-air mixtures be maintained at specific desired levels and that there is a uniform mixture.
It is also important that the combustor parts be adequately cooled due to the high temperatures found in a gas turbine combustor. One such part is the venturi region of the dual stage, dual mode combustor. Film cooling has been effected in this region on the upstream wall of the venturi throat region but it has been found that introduction of film cooling air in this region has an adverse effect on the uniform fuel-air mixture in this region such that there may be created rich/lean pockets: that is, pockets of unburned fuel or pockets of excess air.
In the upstream combustion chamber fuel and air are premixed for ignition to occur during base load operation in the downstream combustion chamber. It is also important that the mixture profile be flat; that is, a uniform mixture. It is also important that the exact fuel air ratio be employed to improve the low NOx performance of the combustor and that the liner be adequately cooled.